This invention relates to improvements in the administration of fluids to patients by means of lightweight and portable, yet highly accurate, fluid-metering and delivery devices.
The administration of fluids to patients is usually accomplished by gravity forces of the fluids from bottles and plastic bags suspended above the patient, whether it be for infusion in a vein or artery or through a naso-gastric or ostial tube into the gastrointestinal tract. The amount of pressure is varied depending upon the pressure head or the height from the bottle or bag of fluid to the inlet to the patient to overcome venous and/or arterial back pressure.
In order to control the amount of fluid entering the patient, restrictors, such as clamps, are placed on the inlet tubing and fluid is observed to drop from the fluid reservoir into a sighting tube. Drops are counted as the means for achieving some quantitative control. The larger the restrictor clamp tube opening is made, the greater the number of drops and thus the more fluid administered into the patient.
Thus, the above two elements of control have been the standard means for infusing fluid into a patient: pressure on the fluid and restrictors on the inlet tubing to control the amount of fluid administered.
The prior art has utilized these two modes to achieve reasonable levels of accuracy in administering fluids. A large number of devices have been made which elaborate on each of these modes. Pressurizing means have been devised as described in patents to Adelberg, U.S. Pat. Nos. 3,640,277 and 4,043,332 to Metcalf which disclose the use of gasses and liquids to pressurize the fluids to be administered. Also, a pressure cuff has been described to squeeze blood through a fixed diameter orifice. Reservoirs of carbon dioxide, air, and other gasses have been described as pressurizing means to squeeze the fluid to be administered and thus to overcome the need for hanging up the fluid to achieve the pressure head of gravity.
Still another group of pressure-driven devices utilizes portable electronic devices in the form of vests, such as described in U.S. Pat. No. 4,087,864, which allow for the solution bags to be carried by the patient and administered by electrically-driven or pressure-drive pumping devices.
All of the above proposed devices provide for complex electronic, electrical, mechanical or electromechanical devices and a number violate the currently accepted practice of the maintenance of sterility of the liquid from the fluid reservoir to the patient to reduce sepsis. Also a great emphasis has been placed in the above described prior art devices on the need for accuracy of administration, i.e., metering, thus incorporating into these devices highly complex means for achieving such accuracy. The commonly used mechanisms for metering volumes of fluid are by syringe types of dispensers, wherein a syringe is filled and expelled. These are referred to as volumetric pumps. Another commonly used mechanism is where a tube is rolled, the space in the tube being fixed in volume, the device being called a peristaltic pump, because of the wave-type action.
Other means for fluid metering have been proposed, such as in U.S. Pat. No. 3,292,824 to Arp et al and U.S. Pat. No. 3,370,759 to Johansson, which utilize a floating piston and various direction-changing devices.
All of these mechanisms incorporate moving parts, some of which touch the liquids to be administered, and most cannot meet stringent sterility requirements.
At the present time, a growing number of patients may now live on intravenous solutions for all of their lives, such as in the case of patients with the short-gut syndrome. Also, the introduction of new jejunostomy feeding tubes and new long-term nasogastric feeding tubes permits the carrying of fluids and the assumption of more normal modes of life, such as being able to go back to work, even though fluids are being administered. A number of patients can be ambulatory even though they are using cancer-chemotherapeutic drugs, anticoagulation drugs such as heparin, nutrients such as elemental diets and protein foods which avoid the necessity of using the body's normal digestive function. The need for a very simple, inexpensive, lightweight, yet accurate means of infusing liquids, will allow patients to leave the hospital at a great cost savings to society.